In the cartridge of the Von Behren patent, magnetic recording tape is driven by a thin, continuous, flexible, pretensioned belt which in turn is driven by a single reversible drive motor that provides rapid acceleration and deceleration of the recording tape in either direction. In such a cartridge, pressure is exerted by the belt on the tape pack over an extended area, and the pressure arises solely from the tension in the belt.
Since the development of the belt-driven cartridge by Von Behren in 1972, there has been a continuing effort to develop cartridges which have a higher storage capacity than that of the original Von Behren cartridge. The cartridge of the Von Behren patent operated at tape transport speeds of about 30 in/sec (76 cm/sec) with a linear recording density of about 1600 flux reversals per inch (630 per cm), and a total storage capacity of about 3 Megabytes. By the early 1980s the total storage capacity had been expanded to 67.5 Megabytes (formatted) by using a thinner tape (which increases the amount of the tape that will fit in a cartridge), a tape speed of 90 in/sec (230 cm/sec), and a recording density of 10,000 flux reversals per inch (3,900 per cm). This new tape had a much finer surface texture than the old tape, in which average surface asperities were about 22 nm, compared with over 100 nm for the old tape. The higher tape speeds and recording densities of the newer tapes required intimate tape-to-head contact and improved uniformity of tape speed to avoid data handling errors. Intimate tape-to-head contact requires uniform tape tension, which in turn requires good contact between the drive belt and tape pack.
In 1984, a new textured drive belt having a microscopically rough surface was disclosed in U.S. Pat. No. 4,466,564 (Smith). The textured belt surface provided for better traction at the belt/tape interface, enabling higher and more stable tape tension at increased tape speeds. The textured belt allowed air molecules to rapidly escape from between the belt and tape during high speed tape winding. This reduced hydrodynamic "lift-off," much like ordinary tread on an automobile tire prevents hydroplaning on wet highways.
Since 1984, the effort to increase the storage capacity of data cartridges has continued. Today's data cartridges have a total storage capacity in excess of a Gigabyte (formatted), a tape speed of 120 in/sec (305 cm/sec) and a recording density of 50,000 flux reversals per inch (20,000/cm).
The data cartridges of tomorrow are expected to have tape with a surface texture in which average surface asperities are less than about 10 nm. This smoother tape will require even better contact between the drive belt and tape pack. Data transfer rates could be increased by increasing tape speed beyond 120 in/sec (305 cm/sec). Similarly, access time to read any file on the cartridge could be decreased by searching the tape at higher speeds.
Increased tape speed will generally result in higher tape acceleration and deceleration rates when the cartridge is used in the start-stop mode. If a computer is unable to read data on a tape at the same rate that the tape is traveling, the computer may store the data in a buffer until it catches up with the tape. However, once the buffer is full, it is necessary to stop the tape. This usually necessitates reversing the tape direction to return to the portion of the tape where the buffer filled up. If the belt is unable to maintain tape tension during rapid decelerations, the tape will continue to unravel from the tape pack due to the inertia of the tape pack, even though the belt has stopped its rotation of the tape hubs. This condition may lead to tape spilling out from the data cartridge and subsequent cartridge destruction. While today's tapes are subjected to accelerations of about 1,500 in/sec.sup.2 (3,800 cm/sec.sup.2), the tapes of the future may be subjected to acceleration rates as high as 3,000 in/sec.sup.2 (7,600 cm/sec.sup.2).
Thus, the cartridges of the future may require smoother tapes, faster transport speeds, and faster acceleration rates. It would be desirable to have a drive belt which provides greater tape tension than currently available belts for tape transport speeds exceeding 120 in/sec (305 cm/sec) at an acceleration of 3,000 in/sec.sup.2 (7,600 cm/sec.sup.2).